Since the creation of paper money, the “war” against counterfeiting has been assigned to very able persons and very capable service departments with all the latest state of the art technology and facilities at their disposal. Counterfeiting has stopped to a large degree, especially from amateur and unorganized counterfeiters.
Although it is not possible to have detailed statistics in the subject concerning counterfeiting and especially in cases of very good quality “fake money” which can pass mostly undetected. In addition, the technology has favored the side of the perpetrators, who have the latest equipment such as scanners, color laser printers and image processing through PCs.
This unfair “war” becomes worse if we assume that counterfeiting can be done by “organized” perpetrators such as extreme groups (but not impossible), an enemy county that desires to damage the economy of their enemy, or even more bazaar (but also not impossible), the country itself in an economical desperation decides to print money with identical serial numbers. Obviously these scenarios are very difficult to follow because, especially in the second case, the control of the currency printing is made by many honest men with integrity and several departments which are staffed with able men. But in every case they remain “men”.
On the other hand, even if we maliciously suppose that the above scenario had been done, nobody would ever be able to prove the counterfeiting existed because the bills were “authentic” and “perfect” that because the “organized” perpetrators had used the same paper, the same printing device, the same ink and technology.
More than that, it is obvious that no government would admit to counterfeiting with the consequence of seeing their economy collapsed.
There is nothing that the organized counterfeiters can not do, except of course from inventing new serial numbers.
They are always forced to use the same serial numbers several times.